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ANS: From 3^1=3, 3^2=9, 3^3=27, 3^4=81, the unit digit repeats in 3-->9-->7-->1-->3. Then, from 3^66=3^(4(16)+2), the unit digt is same as that of ^2. Hence, the answer is 9 and the correct answer choice is E.
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ANS: From ~7^1=~7, ~7^2=9, ~7^3=~3, ~7^4=~1, the units digit is 7-->9-->3-->1-->7, and it repeats like this. Then from 17^381=17^(4(95)+1), we can see that the units digit is same as 17^1, which is 7. The answer is, then, D.
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